1. Field of the Invention:
The present invention relates to a method of generating an RF signal modulated by a message signal and distorted by a predetermined fading profile for testing RF receivers and to a fading simulator for performing the method.
2. Description of the Prior Art
Dispersion phenomena due to multipath distribution in a radio channel lead to so-called fading phenomena at the input of a radio receiver. For the purpose of testing radio receivers in a laboratory under practical conditions, such fading phenomena are produced artificially in a so-called fading simulator. With the conventional fading simulators, the fading phenomena of the radio channel are real-time simulated. The RF signal which is ideally amplitude and/or phase modulated by a message is applied to the input of the fading simulator and this modulated RF signal is baseband converted in the simulator and subsequently subjected to analog-to-digital (A/D) conversion and split into a multiplicity of parallel paths such that an individual path delay and amplitude weighting are formed for each individual path and each path is processed with a non-linear operand for introducing phase and amplitude fluctuations. Thereafter, the individual paths are composed again and the values thus obtained are reconverted into the radio frequency range. In this manner, the phase and amplitude characteristics which correspond to the modulation ar converted into phase and amplitude characteristics which reflect both the modulation and the influence of fading by the radio channel. Known fading simulators require the provision of considerable apparatus and are therefore very expensive. A high signal processing rate is required for a broadband section of the simulated radio channel, whereby the apparatus effort is still more increased due to the necessity for high computing rates.